One major operation in the modern refinery is the process of catalytic cracking. In this process, some of the heavier oils (often called “gas oils”) produced upon fractionation of whole crude oil are decomposed or “cracked” using fluidized zeolite-containing catalysts.
As the supply of light, sweet crude oils has dwindled during past years, catalytic cracking has become increasingly important in maintaining a supply of hydrocarbons suitable for use in various fuels such as gasoline. A problem that has occurred because of the increasing use of heavier, more sour crudes is that the heavier crudes contain substantially more organic metal compounds, such as vanadium and nickel porphyrins. These metals cause many undesirable reactions in heavy oil cracking in that the metals, specifically nickel and vanadium, are quite harmful to the fluidized cracking catalysts used. These metals, present in the high-boiling fractions, deposit on cracking catalyst and accumulate with time. They act as poisons and have the resulting effect of increasing undesirable hydrogen and coke yields, decreasing the selectivity of the catalyst in making liquid products. It is also established that vanadium also attacks the zeolite itself, the high activity component of a catalytic cracking catalyst.
Much effort has been made by those in the refinery/refinery catalyst industry to attempt to deal with the problem of vanadium and other metals poisonous to zeolite-containing catalysts during fluidized catalytic cracking (FCC). U.S. Pat. No. 6,610,255 describes many technologies that have been proposed. The vast majority of these technologies deal with the addition of so-called “trapping agents”, either with the catalyst or with the hydrocarbon feed; and these trapping agents, such as barium, calcium, and strontium have been shown to reduce the deleterious effects of poisonous metals on zeolite-containing FCC catalysts.
In spite of recent developments in FCC catalyst technology, a need still exists for a commercially feasible means for introducing trapping agents during FCC for effectively removing vanadium and other poisonous metals from hydrocarbons.